NSTR MLD Operation Date: - PowerPoint Presentation

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NSTR MLD Operation

Date: 2020-06-10

Authors:

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NameAffiliationsAddressPhoneemailYoung Hoon KwonLiwen ChuManish KumarHongyuan ZhangYan ZhangRui CaoSudhir Srinivasa Hui-Ling LouNXP            

Young Hoon Kwon et al (NXP)

Recap:

Several types of MLDs are discussed:

Multi-Radio MLDSTR MLDNSTR MLDSingle-Radio MLDBaseline single-radio (SR) MLDEnhance single-radio (eSR) MLD

There had been some contributions [1-5] discussing the performance of NSTR MLDs and SR/eSR MLDs.Performance of NSTR MLDs is relatively good in some operation scenarios, but not very impressive in other operation scenarios.

In this contribution, we discuss ways to improve the NSTR MLD operation.Young Hoon Kwon et al (NXP)Slide 2

Observations

Based on discussions and simulation results, NSTR MLDs and SR/

eSR MLDs have following characteristics:NSTR MLDs show significant performance gain over a conventional STA in 1AP/1STA scenario or in low network load scenario.Only slight performance enhancement is expected for NSTR MLDs when there are more STAs associated with an AP or when the network load increases.

eSR MLDs show impressive performance gain when the network load increases.

Young Hoon Kwon et al (NXP)Slide 3

Observations

For operation scenarios that NSTR MLDs do not show performance gain, SR/

eSR MLDs can be a good complement.If a NSTR MLD uses one link only (e.g., due to crowded network) most of times, then it is just a waste of power for the link that is not used.It will be more beneficial if the radios of the unused link to be

Used for the link that is in active frame exchange; orPowered-off at least to save power consumption For example, if a NSTR MLD supports up to N spatial streams (SS) on each link,When the NSTR MLD uses one link only, it would be better if

The NSTR MLD uses 2N spatial streams for frame exchange on the link to improve throughput and latency, orThe NSTR MLD keeps using N spatial streams on the link but power off the radios for the unused link to save power consumptionYoung Hoon Kwon et al (NXP)Slide 4

NSTR MLD vs SR/

eSR MLD

PHY hardware of NSTR MLDs can be easily switched to SR/eSR MLD with minor modification:Multi Radio (NSTR) MLD (e.g., 2x2 radio for each link)

Switch to SR/eSR MLD

Young Hoon Kwon et al (NXP)Slide 52x2RadioLO for CH12x2RadioLO for CH22x2Radio2x2Radio

LO for CH1

LO for CH2

Power off

Proposal

We propose to have a mode of operation that an NSTR MLD on a set of links operates as an SR/

eSR MLD on the set of links.When an NSTR MLD operates as an SR/eSR MLD, the NSTR MLD may have different PHY capabilities compared to those when the NSTR MLD operates normally.Operation mode switchingStatic operation mode switching

Dynamic operation mode switching

Young Hoon Kwon et al (NXP)Slide 6

Static operation mode switching

An NSTR MLD indicates if it would like to operate as an SR/

eSR MLD.After receiving an successful acknowledgement from a serving AP MLD, the NSTR MLD operates as an SR/eSR MLD until another signaling for the operation mode switching is successfully exchanged.One variant of A-Control subfield (e.g., (modification of) OMI A-Control subfield), or management frame exchange (e.g., (modification of) Operating Mode Notification frame exchange) can be used for this purpose.

Young Hoon Kwon et al (NXP)

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Static operation mode switching

Operation example:

A non-AP MLD has 2 links (link1/link2):The non-AP MLD has 2 sets of N radio chains.The non-AP MLD supports reception of N spatial streams (SS) on both links for downlink.The non-AP MLD supports reception of 2N SS on either link1 or link2 for downlink when operates as an

eSR MLD.As the network becomes crowded, the non-AP MLD switches to eSR MLD and utilizes 2N spatial streams on any selected link.A-Control subfield is used for the indication.

With a successful acknowledgement, the non-AP MLD operates as an eSR MLD from the next TXOP.Young Hoon Kwon et al (NXP)Slide 8Link1Link2AP1STA1AP2STA2DATA (#SS=N)BADATA (#SS=N)BADATA (#SS=N)DATA (#SS=N)BA + QoS NullBAStatus change to SR MLDDATA (#SS=2N)BA…Normal operationeSR operationRTSCTSBA

Dynamic operation mode switching

For an AP MLD’s downlink transmission to an NSTR MLD, the following operations may happen:

Case 1: AP MLD obtains TXOPs on multiple links simultaneouslyFor the NSTR MLD, normal operation is beneficial.Case 2: AP MLD obtains a TXOP on one link onlyFor the NSTR MLD, operation as an SR/eSR

MLD is beneficial.Case 3: AP MLD obtains a TXOP on one link first and later obtains TXOP on another linkDepending on the delay, normal operation may or may not be beneficial.

Young Hoon Kwon et al (NXP)Slide 9

Dynamic operation mode switching

Dynamic operation:

If an AP MLD transmits a TXOP initiating PPDUs on both links simultaneously, a non-AP MLD operates normally.If the AP MLD transmits a TXOP initiating PPDU on one link only:The non-AP MLD operates normally until a mode switching event happens.When the mode switching even happens, the non-AP MLD operates as an SR/

eSR MLD until the end of the TXOP.Mode switching event examples:TXOP not initiated on the other link for a given time duration.The AP MLD indicates in a DL frame to switch to SR/

eSR MLD.Etc.Young Hoon Kwon et al (NXP)Slide 10

Dynamic operation mode switching

Operation example:

Same NSTR MLD as the previous example except:Mode switching event is expiration of a Timer (T0) from the initiation of a TXOP on link1.When an AP MLD obtains TXOPs on link1/link2 within T0 time difference, the NSTR MLD operates normally:

When the AP MLD obtains TXOP on link1 and does not obtain TXOP on link2 until T0, the AP MLD does not initiate a TXOP on link2 and exchanges frames with the NSTR MLD using 2N spatial streams on link1.

Young Hoon Kwon et al (NXP)Slide 11Link1Link2RTSCTSAP1STA1AP2STA2DATA (#SS = N)BABusyT0DATA (#SS = N)BALink1Link2RTSCTSAP1STA1

AP2

STA2

DATA (#SS=N)

BA

Busy

T0

DATA (#SS=2N)

BA

Switch to

eSR

MLD

Static vs. Dynamic mode switching

Compared to static mode switching, the dynamic mode switching can:

Switch to SR/eSR MLD adaptively even within a TXOP.Have better overall throughput gain by using more spatial streams on the selected link.Save more power consumption by disabling RF chains during a TXOP.

However, additional complexity is expected for dynamic mode switchingAP MLD needs to know the other link’s behavior near instantly.More stricter switching delay requirement may be needed.Mode switching sequence needs somewhat clarification as it has not been defined yet.

Young Hoon Kwon et al (NXP)Slide 12

Summary

An NSTR MLD can improve its performance or save power consumption if it operates as an SR/

eSR MLD when it operates on a single link.In this purpose, we propose to define a mode of operation that an NSTR MLD on a pair of links operates as an SR/eSR MLD on the pair of links.Operation mode switching can be either static or dynamic.

Young Hoon Kwon et al (NXP)

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SP1

Do you agree to define in 11be SFD a mode of operation that an NSTR non-AP MLD on a set of links can transmit or receive frames on a single link only among the set of links at a time.

Young Hoon Kwon et al (NXP)

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SP2

Do you agree to add the following to 11be SFD: 

The maximum number of spatial streams an NSTR non-AP MLD can transmit or receive on a link when it can transmit or receive frames on a single link only among a set of links at a time can be more than the maximum number of spatial streams it can transmit or receive on the link when it can transmit or receive frames more than one link among the set of links simultaneously at a time.

Young Hoon Kwon et al (NXP)

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References

[1] IEEE 802.11-20-0577r0, RTS and CTS Procedure in

Synchronous Multi-link Operation, MediaTek[2] IEEE 802.11-19-1928r1, Multi-Link Operation Performance Evaluation, MediaTek[3] IEEE 802.11-20-0455r1, Asynchronous multi-link operation for non-STR STA, Intel[4] IEEE 802.11-20-0106r4, Follow up of discussion on multi-link operation with leakage on non-AP MLD, Intel[5] IEEE 802.11-20-0562r2,

Enhanced Multi-Link Single Radio Operation, Intel

Young Hoon Kwon et al (NXP)Slide 16